Perforated acoustical attenuators

Abstract

The invention provides an acoustical attenuator comprising: a porous material comprised of particles sintered and/or bonded together at their points of contact, having at least a portion of pores continuously connected, wherein said porous material has an interstitial porosity of about 20 to about 60 percent, an average pore diameter of about 5 to about 280 micrometers, a tortuosity of about 1.25 to about 2.5, a density of about 5 to about 60 pounds per cubic foot, a modulus of about 12,000 pounds per square inch or above, wherein said porous material has at least one through hole and wherein said interstitial porosity, average pore diameter, density and modulus values are for the porous material in the absence of any through holes, wherein the average diameter of the through hole is greater than the average pore diameter.

We claim: 
     
       1. An acoustical attenuator comprising: a porous material comprised of particles sintered and/or bonded together at their points of contact, having at least a portion of pores continuously connected, wherein said porous material has an interstitial porosity of about 20 to about 60 percent, an average pore diameter of about 5 to about 280 micrometers, a tortuosity of about 1.25 to about 2.5, a density of about 5 to about 60 pounds per cubic foot, a modulus of about 12,000 pounds per square inch or above, wherein said porous material has at least one through hole and wherein said interstitial porosity, average pore diameter, density and modulus values are for the porous material in the absence of any through holes, wherein the average diameter of the through hole is greater than the average pore diameter.   
     
     
       2. The attenuator of claim 1, wherein said through hole(s) have an average length of about 1/8 inch or greater. 
     
     
       3. The attenuator of claim 2, wherein said through hole(s) have an average length of about 1/2 inch or greater. 
     
     
       4. The attenuator of claim 1, wherein said through hole(s) have an average diameter of about 1/64 inch to about 6 inches. 
     
     
       5. The attenuator of claim 4, wherein said through hole(s) have an average diameter of about 1/16 inch to about 2 inches. 
     
     
       6. The attenuator of claim 1, wherein about 0.1 to about 90 percent of the surface area of the attenuator contains through hole(s). 
     
     
       7. The attenuator of claim 1, wherein said through holes are in a symmetrical pattern. 
     
     
       8. The attenuator of claim 1, wherein said through hole(s) cross-section has a shape selected from the group consisting of circular, rectangular, triangular, elliptical, square and slit shaped. 
     
     
       9. The attenuator of claim 1, wherein said through hole(s) are in an asymmetrical pattern. 
     
     
       10. The attenuator of claim 1, wherein the average length to diameter ratio of the through hole(s) ranges from about 1:1 to about 100:1. 
     
     
       11. The attenuator of claim 1 wherein said porous material has a average thickness of about 1/64 inch or greater. 
     
     
       12. The attenuator of claim 1 wherein said material has an average thickness of about 1/2 inch or greater. 
     
     
       13. The attenuator of claim 1 wherein the porous material contains a plurality of through holes. 
     
     
       14. An acoustical system comprising a sound source and an attenuator, the attenuator comprising: a porous material comprised of particles sintered and/or bonded together at their points of contact, having at least a portion of pores continuously connected, wherein said porous material has an interstitial porosity of about 20 to about 60 percent, an average pore diameter of about 5 to about 280 micrometers, a tortuosity of about 1.25 to about 2.5, a density of about 5 to about 60 pounds per cubic foot, a modulus of about 12,000 pounds per square inch or above, wherein said porous material has at least one through hole and wherein said interstitial porosity, average pore diameter, density and modulus values are for the porous material in absence of any through holes, wherein the average diameter of the through hole is greater than the average pore diameter.   
     
     
       15. The acoustical system of claim 14 wherein the sound source is a loudspeaker and the attenuator is a loudspeaker cabinet or loudspeaker housing. 
     
     
       16. A method of of attenuating sound comprising the step of using an acoustical attenuator within an ambient medium, said acoustical attenuator comprising a porous material comprised of particles sintered and/or bonded together at their points of contact, having at least a portion of pores continuously connected, wherein said porous material has an interstitial porosity of about 20 to about 60 percent, an average pore diameter of about 5 to about 280 micrometers, a tortuosity of about 1.25 to about 2.5, a density of about 5 to about 60 pounds per cubic foot, a modulus of about 12,000 pounds per square inch or above, wherein said porous material has at least one through hole and wherein said interstitial porosity, average pore diameter, density and modulus values are for the porous acoustical material in the absence of any through holes, wherein the average diameter of the through hole is greater than the average pore diameter. 
     
     
       17. The attenuator of claim 1, wherein about 0.5 to about 50 percent of the surface area of the attenuator contains through holes(s). 
     
     
       18. The attenuator of claim 1, wherein about 0.9 to about 25 percent of the surface area of the attenuator contains through hole(s).